The Collaborative International Dictionary of English v.0.48:

Interject \In`ter*ject"\, v. t. [imp. & p. p. Interjected; p.
   pr. & vb. n. Interjecting.] [L. interjectus, p. p. of
   interjicere to interject; inter between + jac[e^]re to throw.
   See Jet a shooting forth.]
   To throw in between; to insert; to interpose. --Sir H.
   Wotton.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Interject \In`ter*ject"\, v. i.
   To throw one's self between or among; to come between; to
   interpose. --Sir G. Buck.
   [1913 Webster]

WordNet (r) 3.0 (2006):

interject
    v 1: to insert between other elements; "She interjected clever
         remarks" [syn: interject, come in, interpose, put
         in, throw in, inject]